The invention relates to a double-acting pusher centrifuge comprising a rotatable sieve drum to obtain separation of a mixture into liquid and solid matter portion in the form of filter cakes, a centrally located pusher floor device that is movable to-and-fro along the axis of the sieve drum to push out alternately to one and the other side by an outer annular region the filter cakes, and a central feeding unit to feed fresh mixture in empty spaces formed behind the retreating outer annular region.
Double-acting pusher centrifuges have the advantage that during the pushing-out movement performed by the pusher floor device in one direction in order to push out the filter cake, an empty space is created at the sieve drum on the rear side of the pusher floor into which fresh mixture for filtering may be fed. In the case of correct reversal of the feeding with mixture to the relevant opposite side of the pusher floor device, feeding may proceed continuously. EP 0 068 095 shows double-acting pusher centrifuges having on the pusher floor device a central throughhole, the edge of which is used as a control edge to automatically direct the mixture from a stationary radial feeding means to the front or rear side in dependence on the position of the pusher floor. On both sides is a friction plate connected to the pusher floor proper to form a rotating annular space in which the mixture is accelerated towards the sieve drum. It is essential to ensure that the same amount of solid matter is admitted to the two drum halves before and behind the pusher floor. The axial position of the radial feeding means must therefore be accurately adjusted and the position must be found experimentally by measurement of the two streams of solid matter amounts. In the case of products causing wear, long-term changes in the geometry of the feeding pipe may result in uneven distribution. Furthermore, variations in the amount fed is passed on as uneven distribution. Such variations in the amount may be theoretically reduced by increased throttling at the outlet of the radial feeding means. However, the necessary feed height must be available for such throttling and there is a danger of back damming and blockage, in the case of reduced outlet opening.